Conventionally, a variety of types of a semiconductor acceleration sensor using the MEMS technology is disclosed in the following documents.
[Patent Document 1] JP2006-153519A
[Patent Document 2] JP2001-160626A
[Patent Document 3] JP2004-212403A
JP2006-153519A discloses a technique for a piezoelectric resistance-type three-axis (three dimensional) semiconductor acceleration sensor of two-point-supported type. The piezoelectric resistance-type three-axis semiconductor acceleration sensor includes a MEMS acceleration sensor chip in which thin silicon beam portions support the weight portion (mass) at both sides, the beam portions are distorted when the weight portion (mass) is moved by acceleration, and the acceleration is detected by a variation in the resistance of a piezoelectric resistor formed in the beam portion due to the distortion. In addition, in order to define the excessive displacement of the weight portion (mass) in the upward direction, a stopper plate is provided above the weight portion (mass) with a predetermined gap therebetween. Then, the acceleration sensor chip and the stopper plate are inserted into a hollow package.
JP2001-160626A discloses a technique for a piezoelectric resistance-type semiconductor acceleration sensor of a one-point-supported type. The piezoelectric resistance-type semiconductor acceleration sensor includes a MEMS acceleration sensor chip in which a silicon beam portion supports a weight portion (mass) at one side, the weight portion (mass) is distorted when the weight portion (mass) is displaced in the vertical direction by acceleration, and the acceleration is detected by a variation in the resistance of a piezoelectric resistor formed on the beam portion due to the distortion. In addition, in order to define the displacement of the weight portion (mass) in the vertical direction, stopper substrates are provided above and below the weight portion (mass) with predetermined gaps therebetween.
JP2004-212403A discloses a technique for a piezoelectric resistance-type semiconductor acceleration sensor of a single-hand type. The piezoelectric resistance-type semiconductor acceleration sensor includes a MEMS acceleration sensor chip in which a silicon beam portion supports a weight portion (mass) at one side, the weight portion (mass) is distorted when the weight portion (mass) is displaced in the vertical direction by acceleration, and the acceleration is detected by a variation in the resistance of a piezoelectric resistor formed on the beam portion due to the distortion. In addition, in order to define the displacement of the weight portion (mass) in the vertical direction, a linear stopper is provided above the weight portion (mass) with a predetermined gap therebetween. Furthermore, a cover having a concave portion is provided below the weight portion (mass) with a predetermined gap therebetween, and a protruding stopper for regulating the displacement of the weight portion (mass) in the downward direction is formed in the concave portion.
However, the semiconductor acceleration sensors according to the related art have the following problems.
The both-hand type semiconductor acceleration sensor disclosed in JP2006-153519A includes a plurality of beam portions. When acceleration is detected, the weight portion (mass) is displaced, and the beam portions are bent upward.
At that time, when the stopper plate defines the displacement of the weight portion (mass), the beam portion may collide with the stopper plate by the adjustment of displacement (adjustment of the gap between the MEMS acceleration sensor chip and the stopper plate). In this case, the beam portion may be damaged by the collision.
In addition, in the piezoelectric resistance-type semiconductor acceleration sensor disclosed in JP2006-153519A, a portion of the beam portion in which the piezoelectric resistor is formed is likely to collide with the stopper plate. In this case, the piezoelectric resistor itself and a protective film formed on the surface of the piezoelectric resistor are damaged. When the protective layer formed on the surface of the piezoelectric resistor as well as the piezoelectric resistor itself is damaged, stress applied to the piezoelectric resistor varies, and the characteristics of the piezoelectric resistor are likely to vary.
In the one-point-supported type semiconductor acceleration sensor disclosed in JP2001-160626A and JP2004-212403A, one side of the weight portion (mass) is connected to the beam portion, and the other side of the weight portion (mass) opposite to the one side is opened. Therefore, when the beam portion is bent, the opposite side of the weight portion (mass) is displaced more than the beam portion. As a result, the beam portion is likely to collide with the stopper substrate or the linear stopper.